The invention relates to the managing of a flow of products on a production or assembly line using an accumulator to compensate for variations in the flow of product on the line. The invention specifically relates to controlling a carriage (also referred to as a car) in an accumulator.
A production or assembly line often uses conveyors to move products, such as bottles, cans and boxed items. The lines include stations each of which perform a task associated with the product, such as filling the product package, labeling the product and arranging the products for bulk transport. Conveyors move the products from one station another. Excessive numbers of products do not to gather at any one station, because each subsequent station processes products at least as fast as, and often at least slightly faster than the preceding station.
If an event causes a station to stop or slow, the oncoming products on the line gather at the station. Difficulties arise due to excessive numbers of products attempting to enter the station. To avoid having products gather excessively at a station, it would be helpful to temporarily extend the upstream conveyor to provide additional area along the conveyor to gather products until the stopped or slowed station resumes normal processing of products.
Temporary extensions of conveyors are provided by accumulators. An accumulator is typically an adjustable spur in a conveyor, referred to as the main line conveyor. Products can be moved onto the accumulator to temporarily divert products from the main line conveyor. The accumulator generally includes a pair of side-by-side conveyors operating in opposite directions. Products move along one of the conveyors and are transferred by a carriage to another conveyor before the products are returned to the main line conveyor.
While the carriage is at the front of the accumulator, products move quickly through the accumulator and are returned to the main line conveyor with only a minimal delay due to the accumulator. While the carriage is at the rear of the accumulator, products travel the full length of both conveyors in the accumulator which causes a substantial delay before products are returned to the main line conveyor. The length of the period that products are on the accumulator, and thus off of the main line conveyor, depends on the position of the carriage.
The carriage is moved along the conveyors of the accumulator to adjust the period during which products are on the accumulator and diverted from the main line conveyor. The further the carriage moves from the front of the accumulator, the longer the products remain on the accumulator conveyors and off the main line conveyor. By moving the carriage, the accumulator provides a means for delaying the movement of products along a main line conveyor, and thus delays the movement of products towards a stopped or slowed station.
Accumulators are disclosed in, for example, U.S. Pat. Nos. 4,313,724; 6,497,321, and 8,573,380. These patents describe various techniques for controlling the movement of the carriage and the conveyors in an accumulator. Conventional accumulators typically move the carriage based on the movement of the conveyors or based on manual controls.